•The US government said Hijabi's defection showed the Assad regime is crumbling. The opposition Syrian National Council expressed similar sentiments.

•The Syrian government claimed Hijab, who is a Sunni and was appointed at the end of June, had been sacked and replaced by a caretaker prime minister. Hijab's spokesman dismissed this as a "lie", and urged other officials to follow suit. He claimed Hijab had fled with help from the Free Syrian Army, in an operation that was more than two months in planning.

•The head of the UN monitoring mission in Syria has expressed alarm about the fate of civilians in Aleppo amid reports of more clashes in the rebels. Lieutenant General Babacar Gaye urged both sides to protect civilians.

• Rebels have vowed to fight till the end in Aleppo where the government forced again used aircraft to target rebels positions. Skirmishes were also witnessed in the centre around government buildings and the ancient citadel. Rebels control up to nine tanks in the city, according to a report form Guardian's Martin Chulov in Aleppo.

Iran to host talks on Syria

Reuters reports the deputy foreign minister, Hossein Amir-Abdollahian, as saying: "A consultation meeting on Syria will be held in Tehran on Thursday with the participation of those countries who have ... realistic stances on this country."

The aim of the meeting is to find "ways out of the current crisis, the return of stability and calm to that country and also supporting all constructive regional and international efforts", Abdollahian said.

US echoes opposition SNC over defection

US officials appear to be speaking from the same hymn sheet as the opposition Syrian National Council on the prime minister's defection.

The SNC said it showed the regime was "disintegrating" - a US official also used the word "crumbling" according to AP.

A senior U.S. official says the defection of the Syrian prime minister and other top government ministers is more evidence that the Assad regime "is crumbling."

The American official travelling with Secretary of State Hillary Clinton in Africa called on other senior members of the Syrian government and military to break with President Bashar Assad.

Meanwhile, in Washington, the White House said the defection indicates the momentum is with opposition forces and the Syrian people.

National security council spokesman Tommy Vietor said the defections are reaching the highest levels of the Syrian government and demonstrate that the Syrian people believe Assad's days are numbered.

Vietor said the quickest way to end the bloodshed in Syria is for Assad to recognize that the Syrian people will not allow him to continue in power. And Vietor renewed U.S. calls for Assad to leave power and allow for a political transition.

Chief UN monitor expresses alarm about Aleppo

The head of the UN monitoring mission has expressed alarm about the fate of civilians in Aleppo after a "significant deterioration" of security in the city.

Lieutent General Babacar Gaye's who's mission is due to come to an end on 18 August, issued this statement:

I am extremely concerned about the continued violence in Syria in particular the significant deterioration in Aleppo and its impact on the civilian population.

I urge the parties to protect civilians and respect their obligations under international humanitarian law. Civilians must not be subjected to shelling and use of heavy weapons.I call on all parties to take all necessary steps to open a dialogue as the only way to alleviate the suffering of civilians and bring this conflict to an end.

Head of the UN supervision mission to Syria, Lieutenant General Babacar Gaye. Photograph: Hazim/Xinhua Press/Corbis

Some of the latest video from the city shows the wreckage of a tank and armoured vehicle in the north-west district of Hanano. The video is labelled "dormitory checkpoint" - a reference to the student housing in the background. Graffiti on the tank says "Tawheed" after the rebel brigade leading the fight in Aleppo.

Many houses were levelled, a two-story house was completely destroyed. People are looking for the bodies under the rubble. They can't recover the bodies because of the heavy shooting.

The warplane has also destroyed the media office for Tawheed brigade. The shooting was so heavy that bodies were scattered in the street. The field hospital was also attack. Medical equipment was damaged in the attack.

Summary of the main developments so far on Syria

•Syria's prime minister, Riyad Hijab, has become the highest-ranking official to defect from the Assad regime. His spokesman said he had fled to Jordan with several members of his family, including two brothers who were also ministers. Officials in Jordan confirmed the defection.

•The Syrian government claimed Hijab, who is a Sunni and was appointed at the end of June, had been sacked and replaced by a caretaker prime minister. Hijab's spokesman dismissed this as a "lie", and urged other officials to follow suit. He claimed Hijab had fled with help from the Free Syrian Army, in an operation that was more than two months in planning.

•More clashes have occurred in rebel-held districts of Aleppo, where the Free Syrian Army has vowed to fight till the end. The government has used aircraft to target rebels in the south-western district of Salaheddine. Skirmishes were also witnessed in the centre around government buildings and the ancient citadel. Rebels control up to nine tanks in the city, according to a report form Guardian's Martin Chulov in Aleppo.

We have had tough battles in Aleppo today. All the liberated neighbourhoods which are under the control of the FSA were under attack by the Syrian army. But the army could not regain control.

The Free Syrian Army are in control of 50% of the neighbourhoods in Aleppo. Other districts which are not liberated yet are undergoing heavy fighting right now. We have decided to stay steadfast in Aleppo until the last man we have. We will not withdrew as we did in Damascus [last month]. That was a big mistake. If we pullout now, Aleppo will witness a big massacre like the one committed in Qaboun in Damascus against the civilians after we left. Salahaddine district is completely destroyed. Our men are still there, but it is not under rebel control. We were able to attack two checkpoints in the area.

The district is full of the Syrian army's tanks and the war planes are still targeting the district. FSA are targeting all the police stations in Aleppo now. The city is under an onslaught by the regime for its support of the FSA and military reinforcements keep arriving in Aleppo. We don't know how many people have been killed.

Rebel fighters of the Free Syrian Army hold up their rifles in the northern restive Syrian city of Aleppo, on 3 August. Photo: AFP/Getty Images/Veday Xhysmshiti

Former PM's spokesman urges others to defect

Hijab's spokesman, Mohammad Otri, has urged other ministers to defect, but he warned them to act with caution.

In interview with al-Jazeera English, Otri said Hijab was the highest ranking official to defect so far.

Speaking through a translator, he said: “It will have grave repercussions on the regime and others will follow in his footsteps. Lower ranking ministers have no excuse but to join the revolution.But Otri urged other officials to act with prudence. “The regime will not hesitate in killing anyone and claiming it was the work of terrorists,” he said. He added:

Hijab’s defection had been planned for than two months. Zero hour was delayed on many occasions. By the assistance of the Free Syrian Army he manage to reach a safe haven, and declare his defection. The whole family were taken to a safe place.

Otri said Hijab was given an ultimatum to become prime minister or be killed. He then planned a third option of defecting. Otri, claimed his boss was a popular figure from Deir el-Zour who helped secure the release of political detainees while in office.

Omar Ghalawanji, former first deputy prime minister, on Monday was designated as a caretaker premier.Earlier, former Prime Minister Riyad Hijab was dismissed from his post.

Riyad Hijab is sworn in as Syrian prime minister by President Bashar al-Assad in Damascus on 26 June 2012. He defected to Jordan today denouncing Assad's "murderous" government. Photo: handout/Sana/Reuters.

Hijab's defection statement

I announce today my defection from the killing and terrorist regime and I announce that I have joined the ranks of the freedom and dignity revolution. I announce that I am from today a soldier in this blessed revolution.

Speaking through a translator, Otri quoted the statement as saying: "The country is living under the brunt of genocide and barbarian brutal killing."

Speaking to al-Jazeera, Arabic Otri also claimed that the defection had been planned for months. If true this suggests his smuggling out was being worked up before he was even appointed prime minister in June.

Ahmad Kassim, a senior official with the Free Syrian Army, told AP that Hijab defected to Jordan along with three other ministers. The other ministers' identities were not immediately known, it said.

Sources have told al-Jazeera that several Syrian intelligence officials have defected to Jordan. They include Colonel Yaarab Sharaa, said to be the head of the Damascus branch of Political Security; his brother Lieutenant Kinan al-Sharaa; Colonel Yaser Matar al-Haj Ali; Colonel Dr Ahmad Hassan al-Haj Ali; and Colonel Tawfiq Mohammad al-Haj Ali. They are all under the care of the Jordanian army at a military base, the sources said.

Syrian TV announces sacking of prime minister amid defection reports

Syria TV has announced the prime minster been sacked, amid numerous reports that he has defected.

Reuters reports:

Syrian prime minister Riyad Hijab has been sacked, Syrian television reported on Monday.

President Bashar al-Assad appointed Hijab, a former agriculture minister, as prime minister in June following a parliamentary election in May which authorities said was a step towards political reform but which opponents dismissed as a sham.

Rebels preparing to 'fight to the death' in Aleppo - audio from the city

"We are expecting an imminent large showdown" in Aleppo, according to the Guardian's Martin Chulov in an telephone update from the city.

All last night we were bombed by a circling jet from about 1.30am to 4.30am this morning ... tank fire was thundering into the city as well.

Martin estimates that the rebels control around 60% of Aleppo but are struggling to hold on to the gains they have made. They are pushing into the centre from the east, and there have been fierce clashes around the historic citadel and government buildings, he reports.

They are also trying to win over "hearts and minds" of the populous in the city as law and order breaks down.

Martin expects the rebels to fight to the death rather than flee the city as they have in other areas.

The rebels have secure around 20 "quite primitive" surface-to-air missiles, and they have captured up to nine tanks, Martin said. Their arsenal has been swelled primarily from weapons they have captured, rather than weapons being smuggled in, he added.

Rebel resistance and the extent of their control has surprised Martin since he arrived in the city last Friday.

It is clear that the rebel forces have put more effort into consolidating the city than they did into consolidating their gains in Damascus. There are around 6,000 rebels on the ground here and numbers continue to flow in as they prepare to meet the regime advance. They are going to fight to the death. They do realise that this is an extremely pivotal battle in the whole Syrian uprising, and it could make or break their cause ... the stakes are higher ... if they did leg it this time it would be difficult for them to find a way back. Aleppo is a make or break battle ... I don't think they can afford to cut and run this time.

There has been no sign of foreign fighters in city, as the government has claimed, Martin said. But he reported that rebels do say they have been approached by foreigners offering help.

Civilians have largely fled the east of the city, Martin reported. And in the south-west district of Salahiddine there were no civilians when Martin was there on Saturday night.

(The line to Martin was faint so you might need to turn up the volume on the clip below.)

Aleppo locals seem yet to fully embrace the rebel army, preferring to wait to see who can fill the vacuum.

Abu Suleiman is trying to change that by preparing a letter for locals calling for volunteers to help with civic services, and explaining what role the new sheriff in town intends to play. But as another day ended in war-ravaged Aleppo, the city clearly remained in play. The next week will go a long way towards telling who gets to call the shots.

What began as a peaceful uprising and then became local self-defence has been hijacked. Under Saudi, Qatari and US leadership, and with British, French and Israeli approval, it has turned into an anti-Iranian proxy war.